Lungs and Living Forever

There is a general assumption that if only we could make the cells of our bodies live forever, then so would we. Only cancerous cells are known to divide indefinitely, but groups of such cells do not form structures that are architecturally as sophisticated as the organs ordinarily found in the body. The architecture of the organs is important to the processes these organs perform. So is the behaviour of cells forming these structures. Some cells exhibit quite innocent behaviours that mean that even if cells were immortal, the innate mortality of the organism cannot be avoided.

I am thinking particularly of the lungs.

Even though the lungs are enclosed within the thorax, they are on the front line when it comes to intimate contact with the outside world. We cough out dust, but not all of it. Although they have what might be described as ‘dust-catching’ mechanisms, it is impossible for all dust to be out. It is inevitable that some dust particles will enter deep into the airways.

(Indeed, I remember a cadaver that we were dissecting many years ago. It must have been that of a South Wales miner who, judging from his age, may well have been down the pit in the 1960s or 1970s. His lungs were of the purest, shiniest black that one could imagine. It was as if they had been sculpted from a block of pure anthracite, except that they were soft (even allowing for the embalming process).

The lungs have a mechanism for dealing with those particles that are not coughed out or caught. This mechanism is to wrap them up and form a fibrous barrier around them. Sometimes these packages may even be seen on a chest radiograph – especially if they calcify.

This mechanism has a downside. The process of fibrosis leads to a local reduction in the elasticity of the lungs. This, in turn, makes it more difficult for other particles to be removed and fibrosis progresses. It is conceivable that if we lived long enough, eventually the whole lung would become fibrosed. Certainly, breathing would become increasingly less efficient. If living forever were merely a matter of cells becoming immortal, this (normal) behaviour of lung cells would eventually lead to them becoming unable to sustain life. To prolong life, a lung transplant would be necessary.

The following illustration may add further insight.

From: Roberts, F., & MacDuff, (Eds.). (2018). Pathology Illustrated (8th ed.). Edinburgh. Elsevier.

Gene thinking

The use of the word gene has influenced how we think and speak about heredity. Too often we hear of a ‘gene for this’ and a ‘gene for that’. Given a name, a gene has become a specific thing. The word was first coined in 1909 by Wilhelm Johannsen (1857-1927). In his seminal work, Gregor Mendel (1822-1884) referred only to 'determinants of heredity'. When Johannes coined the term, he had no improved evidence of what the ‘determinants of heredity’ were. He did not know whether they were singular, multiple, situated in one place or distributed and working in concert. Whereas a gene is something specific, a determinant can be an array, a set of factors or even a programme of contributing factors. Mendel’s terminology may still be the more accurate description. At least we can choose to think in Mendel’s terms if the rest of the world uses Johannsen’s ‘shorthand’ term.

Where do breasts belong? (1)

Prologue
In the title for this post, I am using anatomical speech. Breasts come in pairs, of course, so talking of the breast may seem odd. But as with every paired organ in the body, anatomical speech uses the singular. I don’t know why. Talking of ‘each breast’ instead of ‘the breast’ makes sense. In each of the paired organs, the same processes take place irrespective of whether they happen to be on the left or right. And referring to ‘each breast’ also uses the same number of syllables as ‘the breast.’

What I really wanted to focus on was asking to which of the body systems (or physiological systems) does the/each breast belong. As an old professor of mine once put it—quite accurately—the mammary glands (which, with their associated fat, form the basis for the roundness of breasts) are merely modified sweat glands. That makes the milk mammals produce a form of sweat—albeit in a highly modified and nutritious form. (A comparison is worth making with the duck-billed platypus, where the infant licks milky secretions from an area of its mother’s skin rather than from teats or nipples.) Thus, breasts seem to belong quite reasonably to the integumentary system. That, after all, is the system that concentrates on the layers of the skin and associated structures: hair, nails, and the oil and sweat glands.

However, breasts also play a role in reproduction. Without their secretions, offspring would not be able to survive long after birth. Although humans have access to alternatives to breast milk, other mammals do not. So functioning mammary tissue is essential for the survival of offspring. Indeed, can we really call it reproduction or consider reproduction to have properly taken place without some way of ensuring the viability of the offspring? Especially in altricial species such as our own.

Human breasts are also described as secondary sexual characteristics. They develop during puberty in readiness for the reproductive phase in the human life cycle. In so doing, they are also signals of sexual maturity. In this respect, they are also involved in sexual attraction. Thus, they are more than just modified sweat glands.

To return to my original question, does the breast belong to the integumentary system or the reproductive system? Or does the breast overlap with both systems? Or is it an organ not fitting into the current way of defining physiological systems? If this is the case, does this ask questions of the way in which the physiological systems are currently classified? If so, we must consider other ways in which we might conceptualize the human body as a material entity.